1. Field of the Invention
The field of the invention relates to aerial refueling systems generally, and more particularly to certain new and useful advances in Ram Air Turbines (“RAT”), of which the following is a specification, reference being had to the drawings accompanying and forming a part of the same.
2. Description of Related Art
A Ram Air Turbine (RAT) is a small turbine installed in a vehicle to generate electrical power from an airstream created as the vehicle moves through the atmosphere. Typically the vehicle is an aircraft, though RATs have also been used in other types of airborne devices. Some RATs use two-bladed or four-bladed propellers. Other RATs use ducted multi-blade fans. Some low drag ducted RATs slidably enclose a centerbody/valve tube having an aerodynamically shaped nose within a fairing. The tube and nose are movable between positions where the inlet is open as wide as possible or completely closed. Because such a RAT will be deployed directly into the airstream flowing past the host vehicle, its aerodynamically shaped nose is a continuous solid surface from endpoint to the walls of the tube. More importantly, during operation, such a RAT maintains optimum airflow to the turbine blades by moving the tube and nose relative to the fairing. Though this approach is useful, it uses multiple moving parts, which tend to be costly and to require maintenance and/or repair.
Large-extent flight envelopes for RATs can sometimes result in overspeed conditions, where the turbine begins to spin too quickly. If the overspeed condition is not checked, excessive centrifugal forces may damage the turbomachinery—by throwing it off balance and/or by causing the fan blades to crack. Current solutions for mitigating overspeed conditions typically involve variable turbine geometry, as described above, or mechanical braking mechanisms. Either solution is complex and costly.